The present invention relates generally to ground proximity warning systems for use in aircraft. More particularly, the apparatus, methods, and computer program products of the present invention relate to generating a terrain clearance floor envelope about a selected runway for use by a ground proximity warning system to provide appropriate ground proximity warning alerts.
An important advancement in aircraft flight safety has been the development of ground proximity warning systems. These warning systems analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on this analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions with terrain or other obstacles. Further, these ground proximity warning systems ensure that the aircraft maintains a minimum altitude with regard to terrain underlying the aircraft.
For example, one ground proximity warning system has been developed that generates terrain caution and warning envelopes that extend forward of the aircraft based on the position and flight parameters of the aircraft. Terrain and obstacles that pierce the terrain caution and warning envelopes are displayed to the flight crew as potential ground proximity problems by appropriate alarms or warnings. Further, and importantly, the ground proximity warning system also generates terrain clearance floor envelopes that provide minimum altitudes that the aircraft should maintain above terrain underlying the aircraft. If the altitude of the aircraft with respect to the underlying terrain, is less than the minimum altitude required by the terrain clearance floor envelope, the ground proximity warning system will provide appropriate alerts.
These ground proximity warning systems are quite useful in providing the flight crew with information concerning potential problems with the navigation of the aircraft. However, the usefulness of these systems must be balanced against problems associated with providing false alerts to the flight crew that may cause the flight crew to ignore alarms from the ground proximity warning system altogether. For example, during the landing operation of the aircraft, the aircraft will follow a flight path that will eventually intersect the earth at the intended runway on which the aircraft is scheduled to land. In the landing operation, ground proximity warning systems, if not adequately controlled, may generate constant alarms. The constant generation of alarms during landing may be a nuisance due to the added stress and confusion the alarms may impose on the flight crew. Additionally, the nuisance alarms may overshadow other critical alarms in the cockpit.
For this reason, at least one ground proximity warning system has been designed to alter the terrain clearance floor envelopes as the aircraft approaches a selected runway. The terrain clearance floor envelope is altered to reflect a landing pattern of the aircraft. As the aircraft descends toward the runway during landing, the ground proximity warning system provides ground proximity alerts based on the modified terrain clearance floor envelope. As such, the ground proximity warning system provides ground proximity warning protection, while at the same time reducing the number of nuisance alarms.
An example of such a ground proximity warning system is described in the following patents: 1) U.S. Pat. No. 5,839,080 to Muller et al. entitled xe2x80x9cTerrain Awareness System,xe2x80x9d 2) U.S. Pat. No. 4,914,436 to Bateman et al. entitled xe2x80x9cGround Proximity Approach Warning System Without Landing Flap, and 3) U.S. Pat. No. 3,922,637 to Bateman, entitled xe2x80x9cAircraft Landing Approach Ground Proximity Warning System.xe2x80x9d These patents are incorporated herein by reference.
With reference to FIG. 1, the ground proximity warning system described in the above references generates a terrain clearance floor envelope 10 about a selected runway 12. The envelope is typically centered about the selected runway and is typically conical or bowl shaped. The terrain clearance floor envelope has an inner 14 and an outer 22 boundary. As the envelope converges from the outer to the inner boundary, the terrain clearance floor envelope typically decreases in altitude. Further, the terrain clearance floor envelope may include differing slope portions that provide different slopes at different distances from the selected runway. The different sloped portions and their respective distances from the selected runway are chosen to provide desired ground proximity protection, while at the same time reducing the number of nuisance alerts. Beyond the outer boundary, the ground proximity warning system generates a terrain clearance floor envelope 24 that has a constant minimum altitude that the aircraft should maintain above underlying terrain.
An important aspect of the terrain clearance floor envelope is the inner boundary that is proximate to the selected runway. The inner boundary 14 defines a boundary at which the ground proximity warning system ceases to generate ground proximity warning alerts. Cessation in the generation of ground proximity alerts at the inner boundary is important to eliminate the number of nuisance alarms provided to the flight crew during the final approach of the aircraft to the selected runway. The distance between the selected runway and the inner boundary is used to define the distances of the differing slope portions from the selected runway and the location of the outer boundary from the selected runway.
Ideally, the inner boundary would be located as close as possible to the perimeter of the selected runway to thereby provide ground proximity warning protection until the aircraft lands on the selected runway. However, the inner boundary should not overlap with the perimeter of the selected runway, as it may cause the ground proximity warning system to provide nuisance alarms during the final approach of the aircraft. In reality, however, precise determination of the location of the inner boundary may be difficult.
Specifically, the determination of the location of the inner boundary is typically based on the coordinate position of the selected runway and the coordinate position and altitude of the aircraft. However, there are typically data uncertainties associated with the indications of the present position of the aircraft and the coordinate position of the selected runway. These uncertainties make it difficult to locate the inner boundary of the terrain clearance floor envelope in close proximity to the outer perimeter of the selected runway while not overlapping the perimeter of the selected runway.
For this reason, the conventional ground proximity warning system described above typically determines an aircraft position uncertainty factor representing an uncertainty in the coordinate position of the aircraft. The conventional ground proximity warning system typically adds to the aircraft position uncertainty of the aircraft a predetermined buffer distance that is the same for all runways. This added buffer distance is typically 1 nm and is selected to provide a more conservative estimate of the location of the inner boundary, such that the inner boundary does not overlap the perimeter of the selected runway. Additionally, the conventional ground proximity warning system typically locates the inner boundary at a preselected altitude representing a minimum altitude that the aircraft should maintain above underlying terrain at the inner boundary. In light of this selected buffer distance, the distance 16 between the inner boundary and the selected runway defines a region in which the ground proximity warning system does not provide ground proximity alarms. It would be desirable to provide a ground proximity warning system that more precisely defines the location of the inner boundary to thereby not unnecessarily enlarge this region between the inner boundary and the selected runway.
The approach used by the conventional ground proximity warning system to accommodate for errors is somewhat advantageous as it determines the location of the inner boundary based on coordinate positional errors associated with the aircraft, i.e., error in the longitude and latitude. However, this approach fails to account for other determinable errors that may make the determination of the inner boundary more precise. Specifically, the preselected buffer distance used by the conventional ground proximity warning system is not chosen based on the specific factors associated with the selected runway. Instead, it is a predetermined distance used for all selected runways. Further, the conventional ground proximity system does not account for errors associated with the indicated altitude of the aircraft. As it is typically advantageous to define the inner boundary to provide ground proximity warning protection as close to the runway as possible without providing nuisance alarms, it would be desirable to provide a ground proximity warning system that more precisely determines the location of the inner boundary.
As also illustrated in FIG. 1, the conventional ground proximity warning system generates a terrain clearance floor envelope that is circular in shape. While the use of a circular envelope generated about the runway may provide a desired terrain clearance floor envelope for an aircraft approaching the ends of the selected runway, it may not be appropriate for an aircraft approaching the sides of the runway. For instance, with reference to the inner boundary 14 of the terrain clearance floor envelope, the distance between the inner boundary and the ends of the runway, distance 18, is smaller than the distance from the sides of the selected runway, distance 16. As such, the region in which ground proximity warnings are not generated is smaller for the ends of the runway than for the sides of the runway. This is problematic for aircraft that fly crossways over the selected runway or that fly alongside the selected runway instead of approaching from the end of the selected runway.
As also shown in FIG. 1, the conventional ground proximity warning system generates a terrain clearance floor envelope that has a radial cross-section that is the same for all points about the selected runway. Specifically, the terrain clearance floor envelope is typically conical or bowl shaped and has the same cross-sectional slope profile for all portions of the envelope. Further, the cross-sectional profile is selected to reflect a landing pattern of an aircraft at the ends of the selected runway. It is not selected, however, based on a flight pattern of an aircraft that is approaching from a side of the selected runway or is flying to the left or right of the center lengthwise axis 20 of the selected runway. In light of this, it would be desirable to provide a ground proximity warning system that defines the location of the portions of the inner boundary adjacent to the sides of the selected runway differently than the portions of the inner boundary adjacent to the ends of the selected runway.
As set forth below, the apparatus, methods, and computer program products of the present invention overcome many of the deficiencies identified with defining a terrain clearance floor envelope about a selected runway. For example, in one embodiment, the present invention provides apparatus, methods, and computer program products that define a terrain clearance floor envelope based on not only errors associated with the indicated coordinate position of the aircraft, but also on errors associated with the position of the selected runway and errors associated with the indicated altitude of the aircraft. By using error factors associated with the indicated position of the selected runway and the error associated with the indicated altitude of the aircraft, as opposed to a preselected buffer distance, the location of the inner boundary of the terrain clearance floor envelope may be more precisely determined.
The apparatus of this embodiment includes a processor that generates a terrain clearance floor envelope about a selected runway. In operation, the processor defines the terrain clearance floor envelope by at least two boundaries, where at least one of the boundaries is defined by at least one of a runway position quality factor and an altitude data quality factor. In this embodiment, the processor receives either one or both factors concerning uncertainties in the indicated location of the selected runway and/or uncertainties in the indicated altitude of the aircraft. The processor uses either one or both of these uncertainties in determining at least one of the boundaries of the terrain clearance floor envelope.
For instance, in one embodiment of the present invention, the processor defines the inner boundary of the terrain clearance floor envelope based on the summation of the runway position quality factor associated with the selected runway and the altitude data quality factor and position uncertainty factor representing an uncertainty in the indicated altitude and indicated coordinate position of the aircraft, respectively. This, in turn, provides a terrain clearance floor envelope having an inner boundary that is more precisely located with respect to the selected runway to thereby not unnecessarily enlarge the region where no ground proximity warning alarms are generated.
As discussed above, in one embodiment of the present invention, the apparatus and method of the present invention determine the inner boundary based on an altitude data quality factor. In one embodiment of the present invention, the altitude data quality factor is a horizontal distance representing an uncertainty in the altitude of the aircraft. In this embodiment of the present invention, the processor generates the altitude data quality factor by dividing the uncertainty in the altitude of the aircraft by the tangent of a predetermined glideslope angle.
As also discussed, the processor of the present embodiment defines the terrain clearance floor envelope based on at least two boundaries. In one embodiment of the present invention, the processor defines the terrain clearance floor envelope based on both an inner and outer boundary. In this embodiment, the processor defines the inner boundary at a distance from the end of the selected runway equal to the sum of the runway position quality factor, the altitude data quality factor, and the aircraft position quality factor. The processor further defines the outer boundary of the terrain clearance floor envelope at a distance from the end of the selected runway equal to the sum of the runway position quality factor, the altitude data quality factor, the aircraft position quality factor, and a predetermined outer distance representing a predetermined distance from the inner boundary. The processor may also further define the terrain clearance floor envelope by at least one intermediate boundary. In this embodiment, the processor defines the intermediate boundary at a location from the end of selected runway equal to the sum of the runway position quality factor, the altitude data quality factor, the aircraft position quality factor, and a predetermined intermediate distance representing a predetermined intermediate distance from the inner boundary.
In addition to defining the terrain clearance floor envelope based on a distance between an inner and outer boundary, the present invention may also define the terrain clearance floor envelope to have at least one slope decreasing from the outer to the inner boundary to define a landing pattern of the aircraft. In this embodiment of the present invention, the processor first defines the inner boundary to have a preselected inner boundary altitude. The processor also defines the outer boundary to have an outer boundary altitude. The inner boundary and outer boundary altitudes represent minimum altitudes that the aircraft should maintain above terrain underlying the aircraft at the inner and outer boundary distances, respectively. This, in turn, defines a terrain clearance floor envelope that has a slope from the outer to the inner boundary to define a landing pattern of the aircraft. In a further embodiment, the processor may define one or several intermediate boundaries located at different intermediate boundary altitudes. In this embodiment of the present invention, the processor defines a terrain clearance floor envelope having a plurality of slopes from the outer boundary through the intermediate boundaries to the inner boundary to define a landing pattern of the aircraft.
In addition to more precisely defining the inner boundary of the terrain clearance floor envelope so as to not unnecessarily enlarge the region where ground proximity alarms are not generated, the present invention also provides apparatus, methods, and computer program products that define an asymmetrical terrain clearance floor envelope about the selected runway. In this embodiment of the present invention, the apparatus includes a processor that defines the terrain clearance floor envelope such that respective profiles of the envelope in a radial cross-section are different in at least two radial directions from a center point of the selected runway.
Specifically, in one embodiment, the apparatus, methods, and computer program products of the present invention provide a desired landing terrain clearance floor envelope for aircraft approaching the ends of the selected runway, while also providing a desired terrain clearance floor envelope for aircraft approaching the sides of the selected runway. In this embodiment, the processor defines a terrain clearance floor envelope having a different cross-sectional altitude and slope profile for portions of the envelope adjacent to the sides of the selected runway than for portions of the envelope adjacent to the ends of the selected runway.
For instance, in one embodiment of the present invention, the processor defines a portion of the terrain clearance floor envelope adjacent to the sides of the selected runway and proximate to the inner boundary to have a constant preselected altitude. The constant preselected altitude represents a minimum altitude that the aircraft should maintain above terrain underlying the aircraft in this portion of the envelope. This provides a heighten terrain clearance floor envelope for providing ground proximity warnings to an aircraft approaching from the side of the selected runway. The processor of this embodiment also defines a portion of the terrain clearance floor envelope adjacent to the ends of the selected runway to have a slope representative of the landing pattern of the aircraft, such that the ground proximity warning system provides appropriate ground proximity alerts for aircraft approaching the ends of the selected runway.
In addition to defining the terrain clearance floor envelope to have side portions adjacent of the sides of the selected runway with different slopes than portions adjacent to the ends of the selected runway, the processor of the present invention may also define the shape of the different portions of the terrain clearance floor envelope. For example, in one embodiment, the processor may define the shape of the end portions of the terrain clearance floor envelope adjacent to the end of the selected runway to represent various horizontal angles, (i.e., bearing angles), at which the aircraft may land on the selected runway. In this embodiment, the processor defines the end regions of the terrain clearance floor envelope to have a first portion with converging sides that converge from a first width to a second smaller width. This portion of the end region is formed to account for different horizontal angles at which the aircraft may approach the selected runway, (i.e., the bearing angle of the aircraft with respect to the runway). The processor of this embodiment may also define a second portion having parallel sides spaced apart by the second width and extending from the converging sides of the first portion toward the end of the selected runway. This portion of the end region defines an area nearer the end of the selected runway in which the aircraft is typically more aligned with the lengthwise axis of the selected runway on its final landing approach.
In addition to providing a terrain clearance floor envelope having a more precisely located inner boundary and an asymmetrical terrain clearance floor envelope having different cross-sectional altitude profiles, the present invention also includes apparatus, methods, and computer program products that generate a terrain clearance floor envelope having a non-circular inner boundary. For instance, in one embodiment of the present invention, the processor defines portions of the inner boundary adjacent to the sides of the selected runway differently from portions adjacent to the ends of the selected runway. This is important as the processor may locate the portions of the inner boundary adjacent to the sides of the selected runway closer to the sides of the runway than would be possible with a circular inner boundary.
As an example, in one embodiment of the present invention, the processor defines the end portions of the inner boundary as an arc having a radius equal to the sum of a runway position quality factor and an altitude data quality factor from an end point of the selected runway. In this embodiment, the processor also defines the side portions of the inner boundary as lines that are parallel to a lengthwise axis of the selected runway and spaced apart from the side of the selected runway by the sum of a runway position quality factor and an altitude data quality factor. As such, the end profiles of the inner boundary of this embodiment are shaped to accommodate for differing horizontal approach angles that the aircraft may have with respect to the selected runway during landing. Additionally, the side portions are located nearer to the sides of the selected runway to provide increased ground proximity warning protection for aircraft approaching the side of the selected runway.
In addition to providing apparatus and methods for defining the terrain clearance floor envelopes of the various embodiments mentioned above, the present invention also provides computer program products. The computer programs products include a computer readable storage medium having computer readable program code means embodied in the medium. The computer-readable program code means includes various computer instruction means for defining the terrain clearance floor envelopes described above in conjunction with the various apparatus and methods of the present invention.